Radial astrocytes: toxic effects induced by antiepileptic drug in the developing rat hippocampus in vitro

Neuron-glia relationships are crucial for differentiation of both glial and neuronal cells. Interference with these intricate cell interactions could affect regular neuroembryogenesis. In order to analyse potential developmental neurotoxic effects of therapeutically administered antiepileptics such as valproate, we employed organotypic cultures of the rat hippocampus. In these cultures thin tissue slices were continuously rotated between the gas and medium phases, which greatly improved oxygen and nutrient accessibility. This resulted in long-term preservation of the native cytoarchitecture. Exposure of organotypically cultured hippocampi to valproate hampered, in a dose-dependent manner, regular formation of the pyramidal cell layer. Most interestingly, radial astrocytes, which comprise a transient cell population during distinct developmental periods, were selectively affected even by low doses of valproate, but not by structurally related non-teratogenic isomer 2-ethyl-4-methyl-pentanoic acid. The xenobiotic effect did not represent a general gliotoxic insult, since neither the glutathione quotient as determined by HPLC, nor the DNA content, nor the total amount of glial fibrillary acidic protein evaluated by ELISA were significantly altered. Instead, the morphology of astrocytes proved to be the most sensitive index of intoxication with the orientation of radial astrocytes being most affected as revealed by immunofluorescence. In contrast to radial astrocytes, other astrocytic populations proved to be fairly resistent. The data indicate that developmentally regulated cell polarity of astrocytes is a target of therapeutically relevant xenobiotics. This could in turn disturb neuronal differentiation and normal histogenesis.